Arthur tested his new coil-less brush motors and found that it was as quiet as an ocean breeze. It was so quiet that Jin Feng and Jedidiah did not even notice that the motor and fan were turned on! With such an energy efficient motor, there was no need to boost the voltage. 

Subsequently, Arthur, Jin Feng and Jedidiah did acoustic testing for the three blades, and measured RPM and maximum wind speed from a fixed distance away using a fixed motor power of 0.7W.

We found that one of the fans we colloqially referred to as “not best” was the best fan so far, since it delivered the highest wind speed while having comparable sound to “best” fan.

During the evening, we 3D-printed another set of four blades colloqially referred to as “curved”, “best”, “not best” and “long boi”, as well as bottle cap threads for further testing.

We also made some design changes to air cooler bottle prototype 2. On 7 Aug, we included 4 holders on 4 sides of the inner and outer bottle (a total of 16 holders) to install evaporative filters to absorb mist from ultrasonic transducers. On 8 Aug, we incorporated a container in the bottle cap to hold new motor in place, instead of using screws as the motor is very small.